The value of a capacitor is determined by the dielectric constant of the dielectric material used in the capacitor, the thickness of the dielectric material, and the area of the capacitor plates confronting the dielectric material. For a given thickness of a particular dielectric material, a decrease in the effective area of the capacitor plates confronting the dielectric material will proportionally decrease the capacitance value of the capacitor.
At present it is possible to manufacture thin film capacitors on dielectric substrates, typically oxidized silicon wafers. However, it is difficult to produce thin film capacitors of a precise, selected capacitance value. Therefore, it is desirable for a manufacturer to be able to finely adjust the capacitance value of the thin film capacitors during fabrication of the capacitors to achieve a capacitance value within a tighter tolerance than otherwise achievable during fabrication.